Physisorption
Weak adsorption in which molecules are held to a surface by van der Waals forces alone.
Formula / equation
ΔH ≈ −20 to −40 kJ/mol
Unit
kJ/mol
In depth
Physisorption is non-specific, fully reversible, and can build up several molecular layers. Because the forces are weak, it is significant only at low temperature and increases with the ease of liquefaction of the adsorbate. No chemical bonds are formed or broken.
Examples in the real world
Nitrogen physisorbing on charcoal at 77 K, the basis of the BET method for measuring surface area.